VIAGRA
Clinical safety rating: caution
Comprehensive clinical and safety monograph for VIAGRA (VIAGRA).
Sildenafil inhibits phosphodiesterase type 5 (PDE5), increasing cGMP levels in corpus cavernosum, leading to smooth muscle relaxation and blood flow into the penis.
| Metabolism | Primarily hepatic via CYP3A4 (major) and CYP2C9 (minor). |
| Excretion | Renal (approximately 80% as metabolites, 20% as unchanged drug in feces), biliary/fecal (about 13% unchanged in feces). Total clearance 41 L/h. |
| Half-life | Terminal elimination half-life approximately 4 hours (range 3–5 hours). No significant accumulation with recommended dosing. |
| Protein binding | Approximately 96% bound to plasma proteins (mainly albumin and alpha-1-acid glycoprotein). |
| Volume of Distribution | Volume of distribution at steady state (Vss) approximately 105 L (1.5 L/kg for 70 kg adult), indicating extensive tissue distribution. |
| Bioavailability | Oral bioavailability approximately 40% (range 25–63%) due to extensive first-pass metabolism; increased with high-fat meal (delayed absorption). |
| Onset of Action | Oral: 30–60 minutes to achieve erection sufficient for sexual activity; peak plasma concentration at 60 minutes (fasting). |
| Duration of Action | Duration of effect up to 4–5 hours; clinical responsiveness may persist for up to 12 hours in some patients. |
| Molecular Weight | 666.7 |
| Action Class | Phosphodiesterase-V inhibitors |
| Brand Substitutes | Sexigra 100mg Tablet, Vigore 100 Red Tablet, Power Vegra 100mg Tablet, Stimulo 100 Tablet, Silderect Gold 100mg Tablet, Vigron 50mg Tablet, Vigore 50 Red Tablet, Sexigra 50mg Tablet, Stimulo 50 Tablet, Vicogra 50 Tablet |
50 mg orally once as needed approximately 1 hour before sexual activity; range 25-100 mg based on efficacy and tolerability. Maximum dosing frequency: once per day.
| Dosage form | TABLET |
| Renal impairment | CrCl <30 mL/min: sildenafil is not recommended due to increased plasma AUC (100%) and reduced clearance. |
| Liver impairment | Child-Pugh class A or B: initial dose should be 25 mg; consider use only if benefit outweighs risk. Child-Pugh class C: contraindicated. |
| Pediatric use | Not approved for use in pediatric patients; safety and efficacy not established. |
| Geriatric use | For patients ≥65 years: consider an initial dose of 25 mg due to decreased clearance and increased plasma concentrations. |
| 1st trimester | Limited human data; animal studies show no teratogenic effects at clinically relevant doses. Use only if clearly needed. |
| 2nd trimester | Limited human data; no known fetal risk reported. Use only if clearly needed. |
| 3rd trimester | Avoid use in third trimester due to potential for uterine relaxant effects (prolonged labor) and increased maternal bleeding risk. |
Clinical note
Comprehensive clinical and safety monograph for VIAGRA (VIAGRA).
| Placental transfer | Sildenafil crosses the placenta; human data limited but animal studies indicate transfer. |
| Breastfeeding | Excreted into breast milk in small amounts; unlikely to cause adverse effects in infant. However, due to limited data and theoretical risk, caution is advised. |
| Lactation Rating |
■ FDA Black Box Warning
None.
| Serious Effects |
Concomitant use with nitrates (organic nitrates or nitric oxide donors) in any formConcomitant use with riociguat (guanylate cyclase stimulator)Known hypersensitivity to sildenafil or any componentSevere hepatic impairment (Child-Pugh class C)Hypotension (blood pressure <90/50 mmHg)Recent history of stroke or myocardial infarction (within 6 months)Retinitis pigmentosa (genetic retinal disorder)
| Precautions | Risk of hypotension when used with nitrates or alpha-blockers, Caution in patients with anatomical deformation of the penis, Not recommended in patients with cardiovascular disease where sexual activity is inadvisable |
| Food/Dietary | Avoid high-fat meals as they delay absorption and reduce effectiveness. Avoid grapefruit juice which can increase drug levels and ADRs. |
Loading safety data…
| L3 (Moderately Safe) |
| Teratogenic Risk | Insufficient human data; animal studies show no teratogenicity. Risk cannot be excluded; use only if clearly needed. |
| Fetal Monitoring | Monitor maternal blood pressure and heart rate; fetal heart rate monitoring recommended during third trimester if used for pulmonary hypertension. |
| Fertility Effects | No adverse effects on spermatogenesis or fertility observed in animal studies; human data limited. |
| Clinical Pearls | Viagra (sildenafil) is contraindicated with nitrates due to risk of severe hypotension. Onset is 30-60 minutes; duration up to 4 hours. Avoid with alpha-blockers unless stable on therapy. Not for use in women or children. Caution in hepatic impairment, severe renal impairment, and retinitis pigmentosa. |
| Patient Advice | Take approximately 1 hour before sexual activity. · Do not take more than once daily. · Seek immediate medical help if erection lasts >4 hours. · Avoid alcohol and grapefruit juice. · Report sudden vision or hearing loss. · Do not combine with other ED treatments. · Inform your doctor of all medications, especially nitrates and alpha-blockers. |